Not applicable.
Not applicable.
The invention relates to canvas abrasive material and to a process, for the after-treatment of cathodically lacquered surfaces in which the abrasive canvas material is used.
In passenger car manufacture, body sheets are cathodically dip-coated (electro-coating), a base lacquer coat of up to 30 xcexcm thickness being produced. The base lacquer has a certain roughness, to which a further lacquer layer, the so-called filler (primer) adheres well. However, peaks of roughness can occur which stand out beyond the applied primer and are therefore undesired. Such projecting roughness peaks are usually removed by grinding before the application of the primer.
The invention has as its object to provide canvas abrasive material that is particularly suitable for the after-treatment of cathodically lacquered surfaces before the application of primer.
The canvas abrasive material comprises a woven fabric layer with yarns woven in a lattice form and provided with a coating of resin and abrasive grains, giving sufficient stiffness with enough flexibility to conform to the surfaces to be ground. The coated lattice elements form crossing points that determine the grinding plane of the abrasive material; the loading with abrasive grains is thus placed in a grid-like pattern. In order to conveniently hold the canvas abrasive material on a VELCRO-type hand pad or on a grinding disk, a layer of VELCRO-type fabric is applied to the side of the fabric layer opposed to the grinding plane.
The grinding places distributed in a grid pattern form islands in the grinding plane that are respectively surrounded by xe2x80x9cfree placesxe2x80x9d in which the abrasive grains have no effect, since they are set back from the grinding plane. The free places to some extent form, in the grinding plane, gaps into which the roughness peaks of the base lacquer can penetrate, so that they can be caught laterally by the island-form grinding places and struck away (xe2x80x9cbeheadedxe2x80x9d). In this way it is possible to chop the top off only the roughness peaks, without affecting the fine base roughness of the surface.
The thickness of the cathodically applied base lacquer is not always uniform, that is, there are also regions with too thick a lacquer layer. The canvas abrasive material according to the invention is also suitable for processing such densified lacquer layers; that is, to reduce the thickness while producing a fine base roughness that about corresponds to the base roughness of the rest of the cathodically dip coated surface.